Mixed sugar streams, particularly those containing both C5 and C6 sugars, result from hydrolysis of lignocellulosic biomass. Following hydrolysis, these sugars mainly exist in the aldose form. However, ketose isomers of these sugars are typically more amenable to further conversion to useful products and fuels. For example, furans, which form precursors for polymers and hydrocarbon fuels (that could replace gasoline) can be made more easily from the ketose sugars than aldose isomers, and similarly, ethanol can be produced by native yeast through the fermentation the C5 sugar xylose only in its keto-isomer (xylulose) form. As a result, the sugars contained in biomass hydrolysate may need to be converted to their ketose form to facilitate their chemical conversion. The necessary isomerization of aldose to ketose can be achieved by enzymatic (glucose/xylose isomerase (XI)) or chemical (solid acid/base) catalysis. However, the reaction generally favors the aldose form of the sugar and, at equilibrium, only a small portion of the sugar is in the ketose form.
It would be useful to have a system for providing an efficient aldose-ketose transformation and/or separation of C5 and C6 sugars from biomass materials.